For example, composite oxide particles containing cerium and zirconium have been used to polish an oxide film (e.g., a silicon oxide film) constituting a semiconductor device, base materials of the following glass substrates: a base material of a chemically tempered glass substrate such as an aluminosilicate glass substrate; a base material of a crystallized glass substrate such as a glass-ceramic substrate; and a base material of a synthetic quartz glass substrate used as a photomask substrate, or a glass surface or the like of a liquid crystal display panel (see, e.g., Patent Documents 1 and 2).
In order to solve the problems of scratches and dust that arise when polishing is performed with a polishing liquid composition including cerium oxide particles as an abrasive, the polishing liquid composition described in Patent Document 1 includes composite oxide particles in which the secondary particles have an average particle size of 5 μm or less, instead of the cerium oxide particles as an abrasive. The materials of the composite oxide particles include a cerium compound (e.g., CeCl3) and a zirconia compound (e.g., ZrOCl2). The oxidation number of cerium in the cerium compound is 3, and the oxidation number of zirconia in the zirconia compound is 4. The composite oxide particles may be prepared in the following manner.
A cerium compound, a zirconium compound, and ammonia are allowed to react in an aqueous solution to form a water-insoluble compound is subjected to oxidation, filtration, and centrifugal separation, so that a coprecipitate is obtained. This coprecipitate is cleaned repeatedly with ultrapure water etc., dried, and then heat-treated in an oven at an atmosphere temperature of 300° C. or more, thereby providing the composite oxide particles.
On the other hand, the polishing liquid composition described in Patent Document 2 includes composite oxide particles that are produced without a calcining process. Patent Document 2 discloses that this polishing liquid composition can form a surface with high surface accuracy, increase the polishing rate despite a small particle size of the composite oxide particles, and suppress damage such as scratches. The materials of the composite oxide particles include a cerium compound and a zirconium compound. The oxidation number of cerium in the cerium compound is 3 or 4, and the oxidation number of zirconium in the zirconium compound is 4.    Patent Document 1: JP 2001-348563 A    Patent Document 2: Japanese Patent Number 3782771